Abstract:Rockburst is a nonlinear dynamical phenomenon when large amounts of energies release along free surface during excavation within underground rock masses at great depth. An experimental system has been designed to reproduce such a natural rockburst phenomenon by means of two processes,one is true triaxial stress loading process to simulate in-situ stresses;and the other is surface unloading process with unloading one direction stress fast to produce a free surface. During the process of one direction unloading,the stresses in other two directions are kept original or the loads in one direction increase with the other steady. Ten of granite plate specimens are tested. The relation curves of stress and time in the entire process of granite rockbursts are acquired based on the results of collected data. The experimental results show that the process of granite rockburst includes four stages—calm period,small grains ejection,rock flakes and /or grains ejection and collapse entire fracture. Rockburst intensity is defined by the ratio of maximum principal stress s1 to uniaxial compression strength sc. According to the time between the unloading and the beginning of the rockburst,three types of rockbursts are classified,instant rockburst,standard rockburst and delayed rockburst. The microcosmic characteristic of the granite after rockburst fracture is analyzed. Three fracture styles of rockburst are classified—local grains ejection failure,flake spalling failure and block collapse failure. The mechanism of rockburst is preliminarily discussed. It is of great importance to study rockburst mechanism and to prevent rockburst in deep coal mine engineering.